The specific aims of the proposal research are 1) to determine the phase transition and phase separation behavior of liposomes with transmembrane asymmetry similar to that of natural membranes, 2) to determine the effects of purified membrane enzymes on lipid organization and lipid thermal behavior and 3) to determine the effects of transmembrane lipid asymmetry on the enzymatic activity of purified membrane enzymes. Asymmetric liposomes will be prepared using phospholipid exchange proteins and studied by nmr and esr.